Acids and Bases Acids Acids have a sour taste Some acids are very corrosive Acids react with metals to produce hydrogen gas Acids react with bases to produce salt and water Acids turn blue litmus paper red Many foods such as lemons, oranges, tomatoes, vinegar and lemonade contain acids.

Common Acids Hydrochloric acid-manufacture of iron, chemicals and in oil recovery Nitric acid- manufacture of fertilizers, dyes, drugs and explosives Sulfuric acid- manufacture of fertilizers, paints, drugs, detergent and paper, petroleum refining and metallurgy.

Common Acids

Common household acids Citric acid- present in citrus fruits, used in food industry and manufacture of pharmaceuticals Carbonic acid- present in fizzy drinks such as coke, fanta, sprite, solo etc Acetic acid- found in vinegar, used in making other chemicals, including aspirin

Bases Bases have a bitter taste. They are soapy or slippery to touch. They have a chalky consistency. Some bases such as caustic soda can be highly corrosive. Bases turn red litmus paper blue Bases that dissolve in water are called alkalis. Some common bases are soap, toothpaste, detergent, dishwashing liquid and cloudy ammonia.

Common Bases Caustic soda ( sodium hydroxide )- as a cleaning agent and in the manufacture of soap Ammonia- manufacture of fertilizers and cleaning agents Baking soda ( sodium bicarbonate ) – to make cakes rise when they cook

Common Bases

Indicators Acid base indicators are substances that can be used to test whether a substance is an acid or a base. Acid base indicators react with acids and bases and produce a different colour in each. Some indicators are natural dyes while others are artificially made.

Indicators Indicator Colour in Acid Colour in Base Methyl orange yellow Litmus (made from lichens) red blue Bromothymol blue Bluish-purple Phenolphthalein colourless pink Red wine green Red cabbage juice

The pH Scale You can describe how acidic or basic a substance is by using the numbers on the pH scale. The pH scale ranges from 0 to 14 Numbers 0 to 6.9 represent acids. Lower the number stronger is the acid. Numbers 7.1 to 14 represent bases. Higher the number stronger is the base. Substances with a pH of 7 are neutral. Pure water is neutral.

The pH Scale pH can be measured using a pH meter or a special indicator called Universal Indicator. Universal Indicator is a mixture of indicators and changes colour as the strength of the acid or base changes. The universal indicator turns pink in strong acid, blue in strong base and green in neutral solution.

The pH Scale

The pH Scale

Acids and Bases at Work Antacids Stomach contains Hydrochloric acid (pH-1.5) which helps food digestion. If the stomach produces too much acid, it can rise up the food pipe and cause heartburn. The treatment for this indigestion is to take an antacid powder, tablet or liquid. Antacid contains a base which neutralises the excess acid in the stomach and relieves the pain.

How an antacid works? Antacid + Acid = Salt + Water Magnesium Oxide + Hydrochloric acid = Magnesium Chloride + Water

Acids and Bases at Work A sting from an ant or a bee is very painful as it contains formic acid. This can be neutralised by using a base like soap. A wasp sting is painful because it contains a base and can be treated by applying an acid such as vinegar. Some plants grow better in acidic soils while some others require basic soils. The pH of the soil can be changed by adding chemicals to it.

Acids and Bases at Work When the soil is too acidic – lime added When the soil is too basic- ammonium sulphate added Chlorine is added to swimming pool water, it reacts with the water to produce hypochlorous acid which kills the bacteria and algae and makes the pool water safe for swimmers.

Acids and Bases at Work Acids can be used as preservatives to kill bacteria, foods such as onions and beetroot are preserved by storing them in vinegar. This is called pickling. Acids in fizzy drinks and some foods can damage tooth enamel and cause the tooth to erode. Acid rain contains sulfuric and nitric acids dissolved in rain water which can damage buildings, plants and even animals.